Nine 'modern-day slaves' who were freed by police following a dawn raid on a Traveller site in the UK over the weekend have refused to co-operate with the investigation.

Meanwhile, detectives are continuing to unravel what they believe is one of the worst cases of forced labour in modern British history.

Bedfordshire police insist they have dismantled a slavery ring operated by a "family-run organised crime" syndicate that forced vulnerable men to live in appalling conditions for little or no pay.

Four men, all from the same family of Travellers, were charged yesterday with slavery offences relating to four people found at the site in Bedfordshire.

The maximum penalties for such offences range from seven to 14 years in jail.

The men charged have been named as Tommy Connors (30), Patrick Connors (19), James (Big Jim) Connors (34) and James (Jimmy) Connors (23) -- all of Greenacres caravan site, in Great Billington, Leighton Buzzard.

Officers swooped on the site in the early hours of Sunday morning after months of undercover surveillance work sparked by a tip-off.

They expected to find eight people but were instead confronted by 24 British and eastern European men living in filthy buildings ranging from dog kennels to sheds and horse boxes.

Detectives say gang masters targeted the men at soup kitchens, job centres and benefit offices with the promise of work -- but instead subjected them to a gruelling regime, shaving their heads on arrival and forcing them to work for more than 12 hours a day for minimal wages.

The youngest of those rescued is a 17-year-old boy who has been returned to his parents. At least one of those forced to work at the camp had been living there for 15 years.

But in an indication of how many of the men had been institutionalised by their conditions, police yesterday admitted that nine of those rescued had declined to co-operate with the investigation.

One of the men even returned to the Traveller site yesterday insisting that he had been happy to work there and that the police raid had been "heavy-handed".

Experts working to combat slavery said it was often common for victims to empathise with their abusers.

"We can't prejudge what has happened here," said Paul Donohoe, of Anti-Slavery International.

Warnings

"But institutionalisation can create a situation where captives psychologically identify with their captors."

Initial reports suggested that police had been warned 28 previous times that captives were being held at the site.

Yesterday officers stressed that such information had been a misunderstanding and said the investigation was sparked after captives escaped in April.

The remaining 15 men who were rescued were being assessed at a medical centre.

Some of those saved are so badly malnourished that a full meal could prove fatal until their bodies adapt.

A heavily pregnant woman was released on bail yesterday and officers are still trying to track down two more men in connection with the offences.

The raid was one of the first of its kind to use new anti-slavery legislation.

Barbara Young, who tabled the amendment that brought in the new laws, said: "In an ideal world it wouldn't need to be used at all but sadly slavery is real and occurs in the UK."